On 12/21/2022 1:54 AM, Michael Albinus wrote:
> And when they want to use another value? (null-device) returns
> "/dev/null" for local default-directory's if you're not on MS
> Windows. On MS Windows, it returns "NUL".

Right. The intent is for the virtual name for the null device to be the 
same in Eshell no matter what the system really calls it. On non-MS 
systems, this shouldn't actually be necessary, since you could just 
write to the *real* /dev/null. The virtual target in Eshell is just so 
that /dev/null also works on MS Windows/DOS.

However, I would have thought that you could write to NUL on MS Windows 
without any special handling. The Emacs manual has this to say:

"[On MS Windows,] referencing any file whose name matches a DOS 
character device, such as NUL or LPT1 or PRN or CON, with or without any 
file-name extension, will always resolve to those character devices, in 
any directory. Therefore, only use such file names when you want to use 
the corresponding character device."

I'd expect that to mean that if you opened a buffer and tried to save it 
as "NUL", it would just work, but instead I get:

   Write error: Bad file descriptor, c:/NUL

With that in mind, here are two patches (one for 29 and one for master) 
to let Eshell handle both "/dev/null" and (on MS systems) "NUL". That 
way, users get the best of both worlds.